1. Field of the Invention
The present invention relates generally to a temperature sensor provided with adjusting means for modifying manufacturing variations and a method of adjusting the same, and more particularly to a temperature sensor for use in a temperature-compensated crystal oscillator intended to be mounted on small-sized electronic equipment such as cellular phones and a method of adjusting the same.
2. Description of the Related Art
Electronic equipment having a temperature compensating function, such as a temperature-compensated crystal oscillator intended to be mounted on cellular phones, has to be provided with a temperature sensor which detects a variation in temperature to provide an output in the form of a variation in an electrical characteristic.
A typical temperature sensor is one using the pn junction of a diode for example, which has a satisfactory detection accuracy but entails a problem in that it must be used as an external component due to its inability to be incorporated into an IC.
Therefore, another type of temperature sensor is also available which detects temperature through the provision, in analog representation, of an output from an oscillating circuit having a temperature-dependent oscillating frequency. However, this method may result in increased costs and in generation of phase noises.
A temperature sensor used in a conventional temperature-compensated type crystal oscillator comprises, as disclosed in Japanese Patent Laid-open Pub. No. 61-88119 for example, a constant current circuit and a ring oscillating circuit driven by an output from the constant current circuit, the ring oscillating circuit including a plurality of integral delay circuits and a plurality of inverters connected in series with the integral delay circuits, each integral delay circuit consisting of a plurality of resistors and capacitors having certain temperature coefficients.
In order to ensure the output of accurate temperature information by use of such a conventional temperature sensor, it is necessary to keep the temperatures of the resistors and capacitors of the integral delay circuits the same, with the same temperature coefficients.
Although various types of temperature sensors for use in the temperature-compensated crystal oscillator have been put to practical use without being limited to the above example, the temperature coefficients of the resistors and capacitors suffer from manufacturing variations since they are industrial products.
Further, in the case where the temperature coefficients of the resistors and capacitors have deviated from the standards due to manufacturing variations, it is impossible to make the temperature sensors conform with each other through adjustment, resulting in reduced yield and in increased production costs because of severe manufacturing conditions.
Furthermore, the temperature sensor used in such a temperature-compensated type crystal oscillator has often subjected the electronic equipment mounted with the same to an excessive load, namely, a fingerprinting of the temperature sensor using a thermostatic bath, which brings about a further increased cost.
In addition, due to strict phase noise restrictions in the case of an oscillator mounted on a cellular phone, such an oscillating-type temperature sensor is difficult to use as the temperature sensor for temperature compensation therein, since it generates phase noise.
The present invention was conceived in order to solve the above problems. It is therefore the object of the present invention to provide a temperature sensor allowing the detection of temperature without providing the oscillating circuit which is capable of outputting accurate analog temperature information through the adjustment of the manufacturing variations without adding to production costs, and to provide a method of adjusting the same.